Nanomaterials show promise as energy boosters

PORTLAND, Ore.  Lithium-ion batteries could get a twofold boost in charge storage capacity from a nanotechnology developed at the Department of Energy's Argonne National Laboratory and announced May 8 at the 211th Meeting of The Electrochemical Society (Chicago).

Separately, Georgia Institute of Technology researchers, working with their counterparts at Xiamen University in China, have devised a tetrahexahedral (24-facet) nanocrystal that they claim can increase the catalytic activity per unit area in fuel cells as much as fourfold.

In April, another group at Georgia Tech announced a nanomaterial to enable three-dimensional solar cells that would capture nearly all the energy from sunlight, rather than reflect part of it. That could boost the efficiency of photovoltaic (PV) systems while simultaneously reducing the systems' size and weight, according to Georgia Tech.

Argonne researchers Chris Johnson, Naichao Li, Christina Lefief, Jeom-Soo Kim, Jeremy Kropf, John Vaughey and Michael Thackeray presented a paper titled "Anomalous Capacity and Cycling Stability of Layered-Layered Electrodes in Lithium Batteries" at the Chicago meeting. They described a nanocrystalline, layered-composite material for the positive electrode of a lithium-ion battery that increased the charge storage capacity to 250 milliampere-hours/gram.

The Georgia Tech-Xiamen team, led by Zhong Lin Wang in Georgia and Shi-Gang Sun in China, reported producing polycrystalline platinum spheres, measuring about 750 nanometers in diameter, which were then electrodeposited onto a substrate of amorphous carbon. After a chemical treatment, the nanocyrstals were subjected to a 10- to 20-Hz square wave, which converted the spheres to tetrahexahedrons in an electrochemical oxidation-reduction reaction. The conversion enhanced the uniformity of the nanocrystals and boosted their catalytic abilities, according to the team.

The 3-D solar cells developed by senior research engineer Jud Ready at Georgia Tech were fabricated by growing arrays of carbon nanotubes 100 microns tall, 10 microns apart and 40 microns x 40 microns square. The nanoscale towers allowed light to descend into the array, where almost 100 percent of it was converted into electricity, instead of reflecting a portion of the incident light, as is the case for conventional flat solar cells.

Ready grew the arrays atop silicon wafers from a thin film of iron patterned with photolithography. Molecular beam epitaxy was then applied to coat the nanotubes with cadmium telluride and cadmium sulfide, which served as the p-type and n-type layers of the photovoltaic cells.